1. Field
This invention relates generally to the field of digital image processing, and more specifically, to the field of video encoding and decoding.
2. Background
The transmission of video over communication channels, either wireless or wired, has become possible with developments that improve the data capacity of communication channels. Moreover, various standards have been established to facilitate the transmission and reception of video using electronic devices with digital storage media, such as mobile telephones, personal computers, personal digital assistants (PDAs), and other electronic devices. Examples of some video standards that enable the transmission of video images over communication channels are Moving Pictures Expert Group-1 (MPEG-1), MPEG-2, and MPEG-4, International Telecommunications Union (ITU) H.263, H.264, which were promulgated by the International Organization for Standardization (ISO). Another standards-forming body of note is the Audio Video Coding Standard Working Group of China (AVS).
In order to provide such video services, the original images must be compressed in a manner that will not exceed the data capacity of a communication channel. For example, in circuit-switched landline telephone systems, the communication channel is physically limited to 64 kbits/second. However, this bit rate is inadequate for the purpose of transmitting a video stream in its raw format with acceptable perceptual quality. However, the manner in which the compression is performed should not sacrifice the perceptual quality of images at a receiver.
In order to balance these two competing requirements, many video encoders use a transform coding technique combined with a motion compensation technique to compress the original video sequence. The transform coding technique is used to remove spatial redundancy while the motion compensation technique is used to remove temporal redundancy.
It is widely acknowledged by those of skill in the art that compression of original images using transform coding and motion compensation techniques is computationally intensive. The number of instructions needed to perform the compression, as measured in MIPS (million instructions per second), is substantial and may consume hardware resources that could otherwise be allocated to other applications. Since the compression is often expected to be performed within small, portable electronic devices, hardware resources to perform these compression techniques may be limited. Hence, there is a present need to reduce the MIPS or hardware requirements of video encoders without unduly degrading the perceived quality of the video image.